Hippocampal pyramidal neurons (area CA1) in rats, 5, 10, 15, 24, 48 and 90 days old were studied by means of the Golgi-Cox impregnation. Using a video-computer microscope the development of dendritic arborisation was analysed and descriptive as well as quantitative data were obtained. During the suckling period (5 and 10 days) the basal dendrites, the main shaft and within the stratum moleculare branching terminal fibers of the apical dendrite were found to develop. At the weaning period (15 and 24 days) the development progressed with proliferation and ramification of the apical dendrite's lateral branches in the stratum radiatum and of its preterminal fibers branching in the stratum lacunosum. The lateral branches of the apical dendrite developed in a consequent order from the neuronal soma towards fissura hippocampi. Adult numbers of dendrites were set in first, followed by elongation and ramification of the fibers. The final number of segments was in the whole dendrite system, except of the main shaft, established before the maximum of the total dendritic length was reached. The afferent fibers termination upon the pyramidal neurons are known to be distinctly divided within the hippocampal layers. Step by step development of the individual groups of dendrites therefore probably eventuates the linkage of afferent fibers in a successive order.